A method for production of recombinant proteins in milk will be developed. A model system using mice will be used in Phase I. This will establish that it is possible to produce novel proteins in milk from mammary tissues. A promoter specific for mammary cells will be used to direct the expression of a test protein that is easily detected. The DNA constructs containing these segments will be injected into mouse embryos. The resulting transgenic mice will be tested for the presence of the new recombinant proteins in their milk. Those constructs that function in the mouse model system will be injected into bovine embryos in Phase II. The resulting transgenic cattle will be tested for the production of recombinant proteins in their milk. This procedure will establish a methodology by which novel cloned proteins can be produced in cow milk on a commercial basis at a fraction of the cost of current tissue culture techniques.